Traditionally in industry, sensing of magnetic field is utilized for control and measurement of: linear and rotary position sensing, gear tooth sensing, and current sensing. In such applications, however, relatively large magnetic fields are needed to avoid interference/error by background magnetic fields, such as the Earth's magnetic field, fields from ferromagnetic objects, and electromagnetic interference (EMI).
Solid-state magnetic sensors have received increasing attention given their inherent advantage in compactness and power efficiency when compared with traditional/complex counterparts such as search coil, flux gate, and superconducting quantum interference detectors (SQUID) and spin resonance magnetometers (the latter two usually need to be operated at low temperature for optimal sensitivity and resolution).
A typical solid-state magnetic sensor operates by converting the magnetic field sensed into a voltage or resistance. Given the nature of the solid-state sensor, the sensing can be conducted in an extremely small, e.g., lithographically patterned, area, which further reduces size and power requirements. The small size of a solid-state element increases the resolution for fields that change over small distances and allows for packaging arrays of sensors in a small enclosure.
Two conventional solid-state magnetic sensors commonly used today are AMR (anisotropic magnetoresistance) and GMR (giant magnetoresistance) devices. While appearing to be competitive in the power-cost comparison, the AMR (anisotropic magnetoresistive) and GMR (giant magnetoresistive) devices are fabricated with magnetic materials that are not as cost effective as Si. In addition, specific processes and dedicated facilities might be required for their fabrication, implying a finite floor of the lowest cost.
On the other hand, use of a vertical Bipolar Junction Transistor (BJT) on bulk Si as a magnetic sensor with potentially lower cost than AMR and GMR devices has been reported. (Vinal., et al. IEEE Transaction on Electron Device, Vol. ED-31, No. 10, p. 1486, 1984). However, the magnetic sensor based on bipolar transistor reported by Vinal is affected by parasitic current due to the vertical structure and subject to magnetic field attenuation near the emitter junction when the metal contact is too close.